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Date: Wed, 18 May 2011 00:18:12 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: shemminger@...tta.com, kaber@...sh.net, netdev@...r.kernel.org,
remi.denis-courmont@...ia.com
Subject: [PATCH net-next-2.6] net: add rcu protection to netdev->ifalias
Le lundi 02 mai 2011 à 15:27 -0700, David Miller a écrit :
> From: Stephen Hemminger <shemminger@...tta.com>
> Date: Thu, 28 Apr 2011 08:43:37 -0700
>
> > On Thu, 28 Apr 2011 10:56:07 +0200
> > Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> >> Four years ago, Patrick made a change to hold rtnl mutex during netlink
> >> dump callbacks.
> >>
> >> I believe it was a wrong move. This slows down concurrent dumps, making
> >> good old /proc/net/ files faster than rtnetlink in some situations.
> >>
> >> This occurred to me because one "ip link show dev ..." was _very_ slow
> >> on a workload adding/removing network devices in background.
> >>
> >> All dump callbacks are able to use RCU locking now, so this patch does
> >> roughly a revert of commits :
> >>
> >> 1c2d670f366 : [RTNETLINK]: Hold rtnl_mutex during netlink dump callbacks
> >> 6313c1e0992 : [RTNETLINK]: Remove unnecessary locking in dump callbacks
> >>
> >> This let writers fight for rtnl mutex and readers going full speed.
> >>
> >> It also takes care of phonet : phonet_route_get() is now called from rcu
> >> read section. I renamed it to phonet_route_get_rcu()
> >>
> >> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> >> Cc: Patrick McHardy <kaber@...sh.net>
> >> Cc: Remi Denis-Courmont <remi.denis-courmont@...ia.com>
> >
> > Acked-by: Stephen Hemminger <shemminger@...tta.com>
>
> Applied, thanks everyone!
I think we probably have to make some fixes, because rtnl_fill_ifinfo()
can access fields that were previously protected with RTNL
Let's see if it's doable, before considering re-adding rtnl_lock() in
rtnl_dump_ifinfo() ?
First step : dev->ifalias
Its late here, I'll continue the work tomorrow.
Thanks
[PATCH net-next-2.6] net: add rcu protection to netdev->ifalias
Avoid holding RTNL in show_ifalias() and rtnl_fill_ifinfo() to
manipulate netdev->ifalias
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
include/linux/netdevice.h | 7 ++++++-
net/core/dev.c | 28 ++++++++++++++++------------
net/core/net-sysfs.c | 13 +++++++------
net/core/rtnetlink.c | 8 ++++++--
4 files changed, 35 insertions(+), 21 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a134d80..09b3df4 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -980,6 +980,11 @@ struct net_device_ops {
u32 features);
};
+struct ifalias {
+ struct rcu_head rcu;
+ char name[0];
+};
+
/*
* The DEVICE structure.
* Actually, this whole structure is a big mistake. It mixes I/O
@@ -1004,7 +1009,7 @@ struct net_device {
/* device name hash chain */
struct hlist_node name_hlist;
/* snmp alias */
- char *ifalias;
+ struct ifalias __rcu *ifalias;
/*
* I/O specific fields
diff --git a/net/core/dev.c b/net/core/dev.c
index 155de20..01e3be0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1035,6 +1035,12 @@ rollback:
return err;
}
+
+static void ifalias_kfree_rcu(struct rcu_head *head)
+{
+ kfree(container_of(head, struct ifalias, rcu));
+}
+
/**
* dev_set_alias - change ifalias of a device
* @dev: device
@@ -1045,24 +1051,22 @@ rollback:
*/
int dev_set_alias(struct net_device *dev, const char *alias, size_t len)
{
+ struct ifalias *ifalias, *new = NULL;
ASSERT_RTNL();
if (len >= IFALIASZ)
return -EINVAL;
- if (!len) {
- if (dev->ifalias) {
- kfree(dev->ifalias);
- dev->ifalias = NULL;
- }
- return 0;
+ ifalias = rtnl_dereference(dev->ifalias);
+ if (len) {
+ new = kmalloc(sizeof(*new) + len + 1, GFP_KERNEL);
+ if (!new)
+ return -ENOMEM;
+ strlcpy(new->name, alias, len + 1);
}
-
- dev->ifalias = krealloc(dev->ifalias, len + 1, GFP_KERNEL);
- if (!dev->ifalias)
- return -ENOMEM;
-
- strlcpy(dev->ifalias, alias, len+1);
+ if (ifalias)
+ call_rcu(&ifalias->rcu, ifalias_kfree_rcu);
+ rcu_assign_pointer(dev->ifalias, new);
return len;
}
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 1b12217..e2acf15 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -281,13 +281,14 @@ static ssize_t show_ifalias(struct device *dev,
struct device_attribute *attr, char *buf)
{
const struct net_device *netdev = to_net_dev(dev);
+ struct ifalias *ifalias;
ssize_t ret = 0;
- if (!rtnl_trylock())
- return restart_syscall();
- if (netdev->ifalias)
- ret = sprintf(buf, "%s\n", netdev->ifalias);
- rtnl_unlock();
+ rcu_read_lock();
+ ifalias = rcu_dereference(netdev->ifalias);
+ if (ifalias)
+ ret = sprintf(buf, "%s\n", ifalias->name);
+ rcu_read_unlock();
return ret;
}
@@ -1265,7 +1266,7 @@ static void netdev_release(struct device *d)
BUG_ON(dev->reg_state != NETREG_RELEASED);
- kfree(dev->ifalias);
+ kfree(rcu_dereference_protected(dev->ifalias, 1));
kfree((char *)dev - dev->padded);
}
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index d2ba259..c8f0a11 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -849,6 +849,7 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
const struct rtnl_link_stats64 *stats;
struct nlattr *attr, *af_spec;
struct rtnl_af_ops *af_ops;
+ struct ifalias *ifalias;
nlh = nlmsg_put(skb, pid, seq, type, sizeof(*ifm), flags);
if (nlh == NULL)
@@ -879,8 +880,11 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
if (dev->qdisc)
NLA_PUT_STRING(skb, IFLA_QDISC, dev->qdisc->ops->id);
- if (dev->ifalias)
- NLA_PUT_STRING(skb, IFLA_IFALIAS, dev->ifalias);
+ rcu_read_lock();
+ ifalias = rcu_dereference(dev->ifalias);
+ if (ifalias)
+ NLA_PUT_STRING(skb, IFLA_IFALIAS, ifalias->name);
+ rcu_read_unlock();
if (1) {
struct rtnl_link_ifmap map = {
--
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